How do you deduce that two vectors are perpendicular?

Two vectors are perpendicular if

How do you describe a null vector ?

The algebraic sum of two co - initial vectors is 16 units. Their vector sum is 8 units and the resultant of the vectors are perpendicular to the smaller vector. Then magnitudes of the two vectors are -

The algebraic sum of two co - initial vectors is 16 units. Their vector sum is 8 units and the resultant of the vectors are perpendicular to the smaller vector. Then magnitudes of the two vectors are -

Given two vectors hati + hatj and hati +2 hatj, the unit vector coplanar with the two vectors and perpendicular to first is :

Given, two vectors are hati - hatj and hati + 2hatj , the unit vector coplanar with the two vectors and perpendicular to first is:

Given, two vectors are hati - hatj and hati + 2hatj , the unit vector coplanar with the two vectors and perpendicular to first is:

s.Given two vectors are i-j and i+2j the unit,vector coplanar with the two vectors and perpendicular to first is